Assessment of risks to ground-feeding songbirds from lead in the Coeur d'Alene Basin, Idaho, USA

Abstract

Previous assessment of ecological risks within the Coeur d'Alene River Basin identified Pb as a key risk driver for ground-feeding songbirds. Because this conclusion was based almost exclusively on literature data, its strength was determined to range from low to moderate. With the support of the US Environmental Protection Agency (USEPA), the US Fish and Wildlife Service collected site-specific data to address the uncertainty associated with Pb risks to songbirds. These data, plus those from the previous Coeur d'Alene Basin ecological risk assessment, were integrated, and risks to ground-feeding songbirds were reevaluated. These site-specific data were also used to develop updated preliminary remedial goals (PRGs) for Pb in soils that would be protective of songbirds. Available data included site-specific Pb concentrations in blood, liver, and ingesta from 3 songbird species (American robin, song sparrow, and Swainson's thrush), colocated soil data, and soil data from other locations in the basin. Semi-log regression models based on the association between soil Pb and tissue Pb concentrations were applied to measured soil concentrations from the previous risk assessment to estimate Pb exposures in riparian and adjacent upland habitats throughout the Coeur d'Alene Basin. Measured and estimated tissue or dietary exposure was tabulated for 3 areas plus the reference, and then compared to multiple effects measures. As many as 6 exposure-effect metrics were available for assessing risk in any one area. Analyses of site-specific tissue- and diet-based exposure data indicate that exposure of ground-feeding songbirds to Pb in the Coeur d'Alene Basin is sufficient to result in adverse effects. Because this conclusion is based on multiple exposure-effect metrics that include site-specific data, the strength of this conclusion is high. Ecological PRGs were developed by integrating the site-specific regression models with tissue and dietary effect levels to create exposure models, which were solved for the soil concentration that produced an exposure estimate equal to the effect level (i.e., the ecological PRG). The lowest PRG obtained for any species' exposure-effect measure combination was 490 mg/kg for subclinical effects due to Pb in the blood of American robins; the highest was 7200 mg/kg for severe clinical effects due to Pb in the blood of song sparrows. Because the lowest ground-feeding songbird PRG was comparable to multiple cleanup goals developed for the basin (i.e., soil invertebrates, wildlife populations, and human health), in addition to the site-specific cleanup level of 530 mg Pb/kg sediment for the protection of waterfowl (USEPA 2002) the USEPA has made a risk-management determination that a site-specific Pb cleanup level of 530 mg/kg in soil would be protective of songbirds in the Coeur d'Alene Basin.

Efforts to standardize wildlife toxicity values remain unrealized

“…These dose–response assessments were typically applied in the detailed or baseline risk analyses to further refine ecological risks. For example, a dose–response analysis of dietary Pb in 3 ground‐feeding songbird species recently was used to aid in the determination of preliminary remediation goals for the Coeur d'Alene River basin in Idaho and Washington (Sample et al 2011). Although the calculated ED20 (9.9 mg × kg −1 × d −1 ) based on a multiparameter logistic model using data from a chicken reproduction study was higher than the reported LOAEL (3.52 mg × kg −1 × d −1 ) or NOAEL (0.35 mg × kg −1 × d −1 ), the resulting calculated soil preliminary remediation goal was comparable to clean up values previously derived for waterfowl and humans, and therefore considered appropriately protective of ground‐feeding songbirds.…”

“…For example, the USEPA Eco‐SSL TRV derivation procedure uses an inferential statistical method (NOAELs and LOAELs), which historically has been standard practice in regulatory ecological risk assessment. However, alternative TRV derivation procedures (i.e., the use of a species sensitivity distribution based on a population level effect concentration, ED x or benchmark dose) have been proposed (USACHPPM 2000; Allard et al 2010) and are now being implemented at a limited number of Superfund sites (Sample et al 2011). In addition, ERAs frequently are unclear (or unstated) about the uncertainty factors used to derive the TRV values (extrapolation from subchronic to chronic exposure duration), and may use different assumed food ingestion rates, body weights, and interspecies scaling factors (Duke and Taggart 2000; McDonald and Wilcockson 2003; DeMott et al 2005).…”

An evaluation of inorganic toxicity reference values for use in assessing hazards to American robins (Turdus migratorius)

“…Some elements, such as Cd, Zn and Se, have been shown to bioaccumulate to high concentrations in earthworm tissue (Helmke et al 1979). Robins may also be at risk of poisoning by elements such as Pb (Bennett et al 2007, Sample et al 2011), which tend not to bioaccumulate in earthworm tissue but are present in the soil within an earthworm's gut. Hazards from soil ingestion and bioaccumulation are applicable to other avian species that…”

“…Some elements, such as Cd, Zn, and Se, have been shown to bioaccumulate to high concentrations in earthworm tissue (Helmke et al 1979). Robins may also be at risk for poisoning by elements such as Pb (Bennett et al 2007;Sample et al 2011), which tend not to bioaccumulate in earthworm tissue but are present in the soil within an earthworm's gut. Hazards from soil ingestion and bioaccumulation are applicable to other avian species that prey on earthworms, such as American woodcock, plovers, owls, kestrels, rooks, thrushes, starlings, and gulls, and to other vertebrates, such as reptiles (snakes), amphibians (toads, frogs, and newts), and mammals (shrews, moles, red foxes, and badgers) (Macdonald 1983).…”

Revisiting the Avian Eco‐SSL for Lead: Recommendations for Revision

“…Further, site-specific risk-based remedial goals for Pb (based on field-collected avian exposure data) that are many times the avian Eco-SSL of Pb have been identified. For example, the lowest preliminary remedial goal identified by Sample et al (2011) for songbirds exposed to Pb in soil in the Coeur d'Alene, Idaho, USA floodplain was 490 mg/kg. This value was comparable to that identified for sedimentexposed waterfowl in the Coeur d'Alene basin (530 mg/kg; USEPA 2002).…”